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Publication Date: 
September 2019

The kelvin is one of 7 basic units of measurement. Australia’s Chief Metrologist, Dr Bruce Warrington from the National Measurement Institute, explains how we measure temperature.

Transcript

Hello again, I’m Doctor Bruce Warrington, Australia’s Chief Metrologist.

Today I’m talking about how we measure temperature. The unit of temperature is actually the Kelvin; zero Kelvin is ‘absolute zero’, and zero degrees Celsius is 273.15 Kelvin. In space the temperature ranges from 2.7 kelvin – the background glow after the Big Bang - to tens of thousands of kelvin at the surface of a star.

In the 1600s Galileo made a device called a thermoscope to measure relative changes in temperature. The first mercury thermometer was invented in the early 1700s.

Today the International Temperature Scale is based on defined temperatures for the melting and freezing points of a set of pure materials, covering 14 to 1400 Kelvin or -260 to 1100 degrees Celsius. This wide temperature range is needed for everything from cryo-storage of tissue samples to heat treatment of turbine blades. 

Here at the National Measurement Institute we can measure temperature to a thousandth of a degree, important for critical applications like accurately monitoring the temperature of the ocean.

Just last year in 2018 the nations of the world agreed to a new definition of the kelvin, based on a fixed constant of nature – the Boltzmann constant. This new definition opens up new ways of measuring temperature today, and will enable more accurate measurements into the future.

Thanks for listening, and stay tuned to hear about the other units of measurement!

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